WHO_HTM_TB_2009_419_9

Priority should be given to achieving adequate ACH using ventilation systems. However, in some settings it is not possible
to achieve adequate ventilation; for example, because of climatic changes (e.g. in winter or during the night) or building
structure, or because transmission of TB would pose a high risk of morbidity and mortality (e.g. in MDR-TB wards). In such
cases, a complementary option is to use upper room or shielded ultraviolet germicidal irradiation (UVGI) devices. This environmental control does not provide fresh air or directional airflow.